BEIJING, May 31 (Xinhua) -- China and Malaysia on Saturday vowed to continue underwater search for the missing Malaysia Airlines jet MH370 "until it is found."

"Both sides agreed to continue to work closely together in the sub-surface search operation for the missing flight in the southern Indian Ocean off the west coast of Australia," said a joint communique issued by the two countries on Saturday.

The Chinese side welcomes Malaysia's commitment to continue the search until it is found, said the communique.

In the communique, visiting Malaysian Prime Minister Najib Razak expressed sincere gratitude for China's support and assistance in Malaysia's efforts to find MH370, which carried 239 people, including 154 Chinese. The Boeing 777-200 aircraft went missing on March 8 en route from Kuala Lumpur to Beijing.

China deployed the largest number of vessels, aircraft and experts in a massive international search for the missing plane, Najib said, calling the scale of China's participation "unprecedented."

Malaysia, China and Australia held a tripartite meeting from May 5-7 to discuss the way forward for the new phase of the search. All countries expressed their commitment for continuous and intensified efforts in the search.

The communique said Malaysia welcomes China's promise to participate in a bathymetric survey using its assets during the transitional phase, which is essential to subsequent underwater search operations.

Malaysia also welcomes China's participation in deploying assets for side scan sonar in future search operations, it said.

Invited by Chinese Premier Li Keqiang, Najib is on a six-day official visit to China from May 27 to June 1.